Re: [LI] user space, kernel space and .........

["CYMM" <cymm@xxxxxxxxxxxx>]

-----Original Message-----
From: skhader@xxxxxxxxxx <skhader@xxxxxxxxxx>
To: linux-india@xxxxxxxxxxxxxxxxxxxxx <linux-india@xxxxxxxxxxxxxxxxxxxxx>
Date: Wednesday, January 12, 2000 10:13 AM
Subject: [LI] user space, kernel space and .........


skhader asked:

>And anybody here knows what are the four levels in
>the Intel
>processors.
>Thanks
>Regards
>    Khader

        
The levels range from PL0 (protection level 0) to PL3.
PL0 is at the top of the hierarchy. A task running at an
inferior Privelege level cannot commandeer resources
assigned to tasks running at a superior PL.

In this way bad programmers can't mess up the operating
system as easily as with DOS.

PL0 is basically the "kernel level"...and "kernel" tasks would
include memory management and interrupts.

PL1 is the "system services" level: scheduling; communications,
etc.

PL2 is the "OS extension" level which non-OS system tasks 
would use.

PL3 is the "application level"

...So a more privileged level can access the segments of a
task at a less privileged; but the reverse is a no no!

In DOS on the 386;  things usually ran in Real Mode: both the 
OS and the apps had a PL0. Applications had real power
to mess up things!!!

Hope this helps.


alain


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